V(D)J RECOMBINATION AND ALLELIC EXCLUSION OF A TCR BETA-CHAIN MINILOCUS OCCURS IN THE ABSENCE OF A FUNCTIONAL PROMOTER

Transcriptional activation of rearranging Ag receptor gene segments ha s been hypothesized to regulate their accessibility to V(D)J recombina tion. We analyzed the role of a functional promoter in the rearrangeme nt of the murine TCR beta-chain locus using two transgenic minilocus c onstructs. These miniloci each contain an unrearranged V beta 8.3 gene . One has a wild-type V beta 8.3 gene, but the other has a V beta 8.3 gene with a promoter mutation that was previously shown to abrogate tr anscription in tissue culture. FACS analysis of thymus and lymph node cells from transgenic mouse lines showed that only the lines with the wild-type V beta 8.3 gene promoter express an 8.3 TCR beta-chain. Cons istent with the protein expression data, V beta 8.3 gene transcripts w ere found only in the transgenic lines with the wild-type promoter. Us ing a quantitative PCR-based assay, it was shown that both types of tr ansgenic lines recombine the V beta 8.3 gene at similar levels. Rearra ngement of the transgenes was normal with respect to thymic developmen t and junctional reading frame. Interestingly, both types of miniloci also underwent allelic exclusion in that recombination was blocked by the expression of a rearranged TCR beta-chain transgene. We conclude t hat a functional V beta gene promoter is not necessary for proper V(D) J recombination to occur.